Coupling for joining ductile iron and plastic pipes

A method for joining together a ductile iron pipe having a ductile iron pipe end and a ductile iron pipe outside diameter and a plastic pipe having a plastic pipe end and a plastic pipe outside diameter, said method comprising:

• (a) providing a coupling comprising:
• (i) a first end that is adapted to accept the ductile iron pipe;
• (ii) a first elastomeric gasket having an inside diameter that is less than the ductile iron pipe outside diameter, said first elastomeric gasket having an outer annular groove;
• (iii) an annular groove adjacent to the first end, said annular groove having a central bead so that said annular groove may receive the first elastomeric gasket;
• (iv) a first engagement portion having an inside diameter that is sized so as to form a friction fit with the outside diameter of the ductile iron pipe;
• (v) a second end that is adapted to accept the plastic pipe;
• (vi) a second engagement portion having an inside diameter that is sized so as to form a friction fit with the outside diameter of the plastic pipe;
• (vii) a transition portion between the first end and the second end, said transition portion having a frustoconical transition surface;
• (b) placing the first elastomeric gasket into the annular groove adjacent the first end of the coupling;
• (c) inserting the end of the plastic pipe into the second end of the coupling;
• (d) pushing the coupling onto the end of the plastic pipe until the end of the plastic pipe extends at least to the termination of the transition portion of the coupling at the inside surface of the second engagement portion;
• (e) inserting the end of the ductile iron pipe into the first end of the coupling;
• (f) pushing the end of the ductile iron pipe into the coupling.